Unfortunately, offshore drilling rigs or platforms, both mobile and fixed, and offshore production platforms located at a considerable distance from land, are subject to explosions and fires. Fortunately such events are infrequent, but when they occur, as they sometimes do, they create a situation of tremendous emergency. Immediate, fast and safe evacuation of personnel is essential to preserve life and limb.
Present arrangements for such evacuation include inflatable or rigid life rafts or other types of escape craft, both powered and unpowered, which must be launched into the sea. The launching of such escape craft not only is somewhat time consuming but also is itself fraught with danger because of both the hazardous condition on the platform itself, e.g. burning oil or gas, and also on occasion hazardous high seas. Under such launching circumstances it is even possible for the escape craft to become entangled with the platform, thus rendering escape almost impossible. Further, the seas sometimes may be covered with a layer of burning oil. The launching of an escape craft into such a hazardous situation, or even drifting thereinto after being launched, is fraught with even greater peril.
Arrangements for avoiding some of the aforementioned difficulties of launching escape craft are disclosed in U.S. Pat. Nos. 3,796,281 and 3,880,254. In both of those arrangements, however, the escape craft eventually is launched directly into the sea which itself may present a dangerous situation.
Arrangements have been devised for escaping from land-based drilling derricks in case of emergency, such as, for example, the cableway arrangement disclosed in U.S. Pat. No. 2,670,890. For an offshore drilling platform, however, such an arrangement is no more practical than the arrangements disclosed in the first two above-mentioned patents, because, again, escape would be into the sea.
Of course, it is known to transfer personnel from one vessel to another while at sea by cableway arrangements, for example such as that shown in U.S. Pat. No. 1,120,866. In such arrangements, however, at least one, and usually both of the vessels are underway or at least maneuverable and not anchored so that they are not maintained at a fixed distance apart. Moreover, the vessels usually are moving up and down because of wave action. As a result, personnel being transferred from one vessel to another by such an arrangement frequently undergo a "dunking". This would be extremely hazardous if the sea was very rough or covered by a layer of burning oil. Although said U.S. Pat. No. 1,120,866 discloses a counterbalance arrangement for automatically tensioning the cableway to prevent undue sagging thereof, such transfer arrangements are only temporary and usually installed under trying circumstances, as when one of the vessels is in distress because of a storm.